Cellulose fibers cross-linked and esterified with polycarboxylic acids



United States Patent f U.S. Cl. 38144 20 Claims ABSTRACT OF THEDISCLOSURE Crosslinked fibrous compositions comprising celluloseesterified with a polycarboxylic acid, which acid meets the followingrequirements: (1) contains no functional groups except carboxyl, (2)contains at least three free carboxylic groups, (3) each carboxyl groupattached to a separate carbon atom, (4) at least two of the plurality ofcarboxyl groups separated by no more than one carbon atom, are preparedby treating fibrous cellulose with said carboxylic acid having varyingamounts of the carboxylic acid function neutralized with an alkali metalhydroxide, ammonium hydroxide or an amine, and heating the treatedcellulose to induce esterification and concurrent crosslinking. Fabricscomposed of such fibers are capable of developing durable creases.

A non-exclusive, irrevocable, royalty-free license in the inventionherein described, throughout the world for all purposes of the UnitedStates Government, with the power to grant sublicenses for suchpurposes, is hereby granted to the Government of the United States ofAmerica.

This invention relates to novel polycarboxylic acid derivatives ofcellulose and to processes for producing the same. More particularly,the invention embodied herein relates to a process for imparting durablewrinkle resistance or so-called Wash-wear properties to cellulosetextiles and to articles fabricated therefrom. It provides a uniquemethod for fixing ironed-in smoothness, ironedin creases, gloss, orluster produced by calendering and other mechanical effects, makingthese physical modifications durable through laundering operations.

An object of this invention is to provide modified celluloses which havesuperior properties when employed as fibers, yarns, fabrics, and films.Another object is to produce crosslinked cellulose compositions whichdevelop no odors and which are chlorine-resistant. An additional objectis to develop ester-crosslinked celluloses which Withstand washes withbuilt detergents in home washers. A further object is to providechemically modified cotton fabrics having improved dye aifinity forcationic dyes and greater retention of cationic finishes. A furtherobject is to produce ester-crosslinked celluloses and cotton cellulosefabrics having improved wrinkle recovery properties and smooth-dryingcharacteristics. A further object is to produce crosslinked cellulosefabrics which exhibit an ability to accept or release creases uponironing creasing treatment at elevated temperatures. A further object isto provide a process for reacting the polycarboxylic acid directly withcellulose at elevated temperatures in an operation which approaches theconventional additive finishing process in simplicity and ease ofoperation.

Patented Sept. 1, 1970 Cellulose esters of various types are known inthe art [D. I. Stanonis, Encyclopedia of Polymer Science and Technology,vol. 3, p. 455, 1965; C. J. Malm, Svensk kemisk tidskrift 73, 523-530(1961)]. A conventional procedure for preparing esters from monoordicarboxylic acids employs the acid chloride in an anhydrous systemdiluted with an amine and an organic solvent [D. J. Stanonis,Encyclopedia of Polymer Science and Technology, vol. 3, p. 455, 1965].Cellulose may be esterified conveniently by employing agents such astrichloroacetic anhydride and triiluoroacetic anhydride in anhydrousorganic media to impel the esterification of the free carboxylic acidwith cellulose [D. I. Stanonis, Encyclopedia of Polymer Science andTechnology, vol. 3, p. 455, 1965 M. D. Cruz-Lagrange, C. M. Hamalainen,and A. S. Cooper, Jr, Am. Dyestuff Reptr. 51 (12) 40 (1962; H J.Campbell and T. Francis, Textile Res. J. 35, 260 (l965))]. Celluloseesters containing free and reactive carboxyl groups in the acid or saltform have been prepared through the reaction of dibasic acid anhydrideswith cellulose in the presence of a catalyst such as pyridine [C. I.Malm and C. R. Fordyce, Ind. Eng. Chem. 32, 405 (1940); F. Schulze to E.I. du Pont, U.S. 2,069,974, February 1937; F. C. McIntire to AbbottLaboratories, U.S. 2,505,561, April 1950], and through the impellingaction of trifluoroacetic anhydride on tricarboxylic monoanhydrides [R.H. Wade to USA, U.S. 3,097,051, July 1963]. Direct preparation of estersof cellulose from diand tricarboxylic acids at elevated temperatures hasbeen limited to a few organic acids [T C. Allen, Textile Res. J. 34,331, (1964); D. D. Gagliardi and F. B. Shippee, Am. Dyestuff Reptr. 52,P300 (Apr 15, 1963)], and has been accompanied by considerable moleculardegradation of the cellulose [D. D. Gagliardi and F. B. Shippee, Am.Dyestufi Reptr. 52, P300 (Apr. 5, 1963)].

A method has been found whereby a new class of crosslinked,polycarboxylic acid esters of cellulose can be made; these constitutenovel crosslinked cellulose compositions, especially valuable in theform of crosslinked cotton cellulose fabrics.

In the process of this invention, a native or regenerated fibercellulose which may be in the form of free fibers, sliver, yarn, threador fabric is contacted with a system comprising a suitable solvent ordiluent, the polybasic acid, and an optional buffer and catalyst. Thereaction between the polybasic acid and cellulose is caused to occur byelevating the temperature of the composition to the range of 250 C. forsuitable curing.

When cellulose is reacted under the preferred conditions, the resultingpartial esters retain the original color, appearance, and fibrous formof the cellulose. These prodnets are insoluble in common solvents suchas water, dilute bases, dilute acids, ethers, hydrocarbons, alcohols,ketones, and the like.

The reagent system can be deposited on the cotton from any solvent inwhich the components are soluble. It is preferred to dissolve thereagents and apply them to cellulose from an aqueous system. Thisassures intimate contact between the insoluble cellulose and thereactants. Other suitable solvents which may be applied together with orto the exclusion of Water are dimethylformamide, dimethylsulfoxide,dioxane, pyridine, acetic acid, and the like solvents.

The concentration of reagents in the solution which is applied tocellulose may vary over a considerable range depending on the solvent ordiluent. In general, it is desirable that the polybasic acid be presentto the extent of 1 to 25% of the total solution. This solution may be deposited on cellulose at any convenient level, but, most generally, tothe extent of 50-150% of the weight of the cellulose. It is inefficientand uneconomical to use the highest proportions of the reagent solutionsof highest concentrations. The ratios of reagent solution to celluloseand reagent to cellulose will depend upon the extent of reaction desiredon the hydroxyl groups of the anhydroglucose units of the cellulosestructure, and the particular properties desired in the final product.It is generally preferred to employ 510% solutions of polybasic acid andto deposit these on the cellulose to the extent of 80-120% of the weightof the cellulose. This will generally introduce 5-15% of carboxylicester into the cellulose.

Polybasic acids which are suitable for this process are those whichcontain three, and preferably more, free carboxyl groups per moleculeand which are free of olefinic unsaturation and hydroxyl groups. Eachcarboxyl group should be attached to a different carbon atom such that amalonic acid type of structure is not involved. Preferably, eachcarboxyl group should be located in the carbon skeleton of the moleculein such an arrangement that it is capable of forming a 5- or 6-memberedanhydride ring with at least one adjacent carboxyl group. Thisrequirement is met when the carboxyl groups are located on adjacentcarbon atoms or separated by no more than one additional carbon atom.One carboxyl group in the polycarboxylic acid may be isolated from theother carboxyl groups and may be excepted from the foregoing requirementto form an anhydride structure with an adjacent carboxyl group.

Examples of specific polycarboxylic acids which fall within the scope ofthis invention are the following: propane-1,2,3-tricarboxylic acid,butane-l,2,3,4-tetracarboxylic acid, hexane-l,2,3,4,5,6-hexacarboxylicacid, cyclopentane-1,2,3-tricarboxylic acid (and the 1,2,4-isomer),cyclopentanetetracarboxylic acid, cyclohexane 1,2,3-tricarboxylic acid(and the 1,2,4-isomer), cyclohexane-1,2,3, 4-tetracarboxylic acid (and1,2,4,5-isomer and 1,2,3,5-iso- 'mer), benzene-1,2,3-tricarboxylic acid(and 1,2,4-isomer), pyromellitic acid, mellitic acid,naphthalene-l,4,5,8-tetracarboxylic acid, biphenyl-3,4,3',4'tetracarboxylic acid, benzophenone-3,4,3',4'-tetracarboxylic acid andthe like.

Although our understanding of the chemistry of the reaction of thesepolycarboxylic acids, as such, in the partial alkali salt form and inthe partial or in the complete amine salt form, is not complete, itappears that the requirement for 3 (preferably 4 or morecarboxyl groups,the location of these carboxyl groups on adjacent carbons (onimmediately adjacent carbons or separated by no more than one morecarbon atom), and the absence of other functional groups such ashydroxyl groups or re active (olefinic) unsaturation are essential foradequate reaction with the cellulose, for effective crosslinking of thecellulose chains for development of high levels of wrinkle resistance,and for amenability to introduction and removal of creases at elevatedtemperatures.

Substantially any strong base capable of forming a soluble, partial saltof polybasic acid in an eifective concen tration in thereactant-containing liquid, can be used as the buffering agent.Illustrated examples of suitable strong bases include: alkali metalhydroxides, carbonates, bicar- "-bonates, acetates, phosphates, borates,ammonia, secondary amines, tertiary amines, quaternary ammoniumhydroxides.

The-proportionate amount of catalysts or buffer conemployed for textilefinishing operations (lubricants, dyes, and the like), provided ofcourse that these agents are compatible with the other reactants. Theproportion of buffer or catalyst is not highly critical and depends uponthe specific polybasic acid being employed, the temperature of cure, andthe desired rate of reaction. Buffer or catalyst to the extent ofapproximately l-l0% of the total solution may be employed effectively.It is generally desirable that the pH of an aqueous reagent system be inthe range of 2.5-5.

The apparatus and handling techniques usually employed for the chemicaltreatment of textile fibers can be employed in the process of thisinvention. In general, the employment of fibers in the form of yarns orfabric is preferred. Examples of fibers which may be employed includecotton, flax, ramie, and the like natural vegetable textile fibers;mercerized, partly acetylated, partially cyanoethylated, partiallybenzylated, or the like chemically modified natural vegetable textilefibers which contain at least one cellulosic free hydroxyl group peranhydroglucose unit; and derived or regenerated cellulosic textilefibers such as the fibers regenerated from natural vegetable textilefibers by the cuprammonium and viscose processes. The natural vegetabletextile fibers are particularly suitable for employment in this process.

At the time the cellulose fibers are wetted with the reagent, thereagent may be mainaitned at substantially any temperature above thefreezing point and below the boiling point. In general, the reagent ispreferred at about room temperature and the step of Wetting the fibersmay be carried out by any convenient method, including a textile padder.In some cases it may be desirable to evaporate the solvent or diluentfrom the cellulose prior to cure at elevated temperature. This may becarried out conveniently at temperatues in the range of 50-100 C.

The temperature at which the reaction between polybasic acid andcellulose is conducted may be varied, depending, for example, upon theparticular solvent and the reactants employed. The rate of the reactionand the particular performance properties desired in the product may becontrolled, to some extent, by the temperature at which the impregnatedcellulose is cured. It is preferred to carry out the reaction above C.in order to obtain rates of reaction which are in a practical range. Theduration of reaction is intimately dependent upon the temperature; avery short exposure to temperatures in the range of ZOO-250 C. issuflicient to react the polybasic acids with cellulose. On the otherhand, an exposure of several minutes at C. is essential for goodreaction, and an exposure of several hours is required for temperaturesclose to 100 C.

The foregoing process is described by way of general illustration of theprocedures for preparation of the compositions of this invention.However, it should be noted that the acid chloride method and theimpeller methods have been generally unsatisfactory for preparing thedesired polycarboxylic acid-modified celluloses.

The invention is set forth in the following paragraphs and examples byway of illustration and not as a limitation.

EXAMPLE 1 A 10 g. sample of 80 x 80 desized, and bleached cotton printcloth was thoroughly wet with a solution of disodiumcyclopentanetetracarboxylate in water; this disodium salt solution wasprepared from the free acid by adding one mole of sodium carbonate foreach mole of cyclopentanetetracarboxylic acid. The treating solution hada pH of 4.5-5.0. The cloth was wrung to a wet pick up of Ill-114%, andcured in a forced-draft oven at C. for 10 min. The fabric was washed inhot running water, dried at 85 C. and allowed to equilibrate in air atthe prevailing humidity. The weight gain shown by the fabric depended onthe concentration of disodium salt in the treating solution, astabulated below:

gain shown by the fabric depended on the number of carboxylic groups inthe cyclopentanetetracarboxylic acid that Concentration Weight AdditionElmendori'. Breaking str. Monsanto wrinkle Rec. (W +F) odium gain,etficienoy, tear str. (warp: 1 in.

salt, percent percent percent (warp) (g.) strip) Obs.) Wet Dry 100)(weight gain 1 Percent eficieucy=- concentrationXwet pick-up The treatedfabrics had enhanced wrinkle resistance in the Wet and dry states, asindicated by the listed wrinkle were neutralized in making up thetreating solution, and are tabulated below.

No. of COONa Weight Addition Elmendorf Breaking Str. Monsanto WrinkleRec. (W+F) groups per gain, efficiency, Tear (warp: 1 in.

molecule percent percent (warp) (g) strip) (lbs.) Wet Dry 1. 0 7. 1 81653 44 222 254 1. 7. 4 89 713 46 210 248 2 2. 0 7. 1 73 700 53 201 2303. 0 2. 7 26 Untreated 0. 0 00 1, 100 58 158 195 lOOXWeight gain 1Addition etficiency= salt concentrationXwet pick-up 2 Data taken fromrun 1 of Example 1.

recovery values and by crumpling tests. The fabrics retained theiroriginal suppleness and were free of discoloration. Fibers of thetreated fabrics were insoluble in 0.5 M cupriethylenediamine solution,showing that the cellulose had been crosslinked by the treatment.

Had the reaction proceeded by disproportionation of the disodium saltinto tetrasodium salt and free tetracarboxylic acid, with only the freeacid becoming bound to the cotton cellulose, the maximum efficiencypossible would have been 42.5%. In all of the above experiments, thereaction efficiency was greater than this, showing that the disodiumsalt of cyclopentanetetracarboxylic acid reacted directly with thecotton cellulose. The breaking strength reained in the treated fabricswas 849l% of that for the untreated fabric, and the tearing strengthretention was 64-73%. The high retention of strength observed is theresult of using the nearly neutral disodium salt, wherein the hydrogenion concentration was only 1 X to 3 x 10 molar, thus avoiding aciddegradation of the cotton cellulose.

EXAMPLE 2 A 10 g. sample of 80 X 80 desized, scoured and bleached printcloth was thoroughly wet with a solution prepared by dissolving 7.4parts by weight of cyclopentanetetracarboxylic acid in 90 parts ofwater; sufficient sodium carbonate was then added to neutralize thecarboxylic acid to the extent indicated in the table below. The clothwas then wrung to a wet pick-up of l09lll%, and cured in a forced draftoven at 160 C. for 10 min. The fabric was washed in hot running water,dried at 85 and allowed to equilibrate in air at the prevailinghumidity. The weight The treated fabrics had enhanced wrinkle resistancein the wet and dry states, as shown by the tabulated wrinkle recoveryvalues and by resistance to manual crumpling. They retained theiroriginal suppleness. Fibers of the treated fabrics were insoluble in 0.5M cupriethylenediamine solution, indicating that the cellulose had beencrosslinked.

In the case where three of the four carboxyl groups of thecyclopentanetetracarboxylic acid were neutralized prior to applicationto the cotton (run 4), the pH of the treating solution was 6.Appreciable reaction and crosslinking still occurred, againdemonstrating that the esterification of cellulose can be conducted inessentially neutral media. The reaction efficiency remained essentiallyconstant as the amount of sodium carbonate added ranged from 0.5 to 1.0mole per mole of cyclopentanetetracarboxylic acid.

All of the treated fabrics were dyed a medium shade by methylene blue inaqueous solution, while the untreated cloth was but slightly coloredafter being washed. The enhanced affinity of the cationic dye for thetreated fabrics indicates that these fabrics contained anionic groups.This established that not all of the carboxyl groups in each molecule ofcyclopentanetetracarboxylic acid are esterified with cellulose.

EXAMPLE 3 Desized, scoured, and bleached cotton print cloth was paddedin solutions containing 7.4% of polycarboxylic acid and varying amountsof sodium carbonate to adjust the pH of the solution. The wet pick-upswere adjusted to the samples were dried for 8 minutes at 80 and curedfor 10 minutes at C. in a forced draft oven. The cured samples of fabricwere washed and then characterized for physical properties. The resultsare summarized in the accompanying table.

Monsanto wrinkle Rec. (W+F) Elmcndorf pH of tear strength Polycarboxylicacid reagent Wet Dry (warp) 1 Cy013pentane-tetracarboxylic 1. 9 225 260480 2 Propane-1,2,3-tricarboxylic 1. 9 233 240 440 acid. 3. 0 217 272570 3 Butane-1,2,3,4-tetracarboxylic 1 5. 0 181 215 690 acid. 6. 7 184880 4 Citric acid 1. 6 229 237 310 5 Aconitic acid 1. 5 219 216 390 Theacid was insoluble without substantial conversion to the sodium salt.

It will be noted from the above data that the maximum of dry wrinklerecovery is realized when the acids are applied as partial sodium salts,which is illustrated in this table for the system having a pH of 3. Atthe lowest PH (which is that characteristic of the free acid) and at thehighest pH (which results from more complete neutralization of the acidwith sodium carbonate), the wrinkle recovery values are significantlylower. In the cases illustrated, substantially less reaction occurs atthe higher pH. While significant reaction of the carboxylic acid occurswith the cotton at the pH characteristic of the free acid, the reactionis accompanied by considerable degradation as indicated by the fact thatthese fabric are characterized by the lowest values of tear strength.

In certain cases, such as illustrated in run 3, the acid is insoluble inthe aqueous system without partial salt formation and cannot be reactedwith the cotton cellulose except in the latter form.

It will be noted that polycarboxylic acids containing functional groupsother than carboxyl groups (see run 4 and run 5 above) performed poorlywith respect to wrinkle recovery. Moreover, the presence of functionalgroups other than carboxyl in the polycarboxylic acid interferesmarkedly with crease removal, which property of the treated fabric is animportant feature of our invention. Coloration also develops in thesemodified cottons.

EXAMPLE 4 Weight gain from reaction Fraction eth-ylamof acid,

of sodium moniurn Polycarboxyllc acid salt salt 1 Nitrilotriacetie acid2 Cyclopentane-tetracarboxylic acid. 3 Mellitic trianhydrlde 4Pyromellitic acid 4 1 5 Benzophenone43,4,3',4- tetracarboxylic acid.

1 Excess basea-.u excess of 35% over the stoichiometric amount.

An examination of the above data shows that the greater degree ofreaction of the polycarboxylic acid with cotton cellulose was realizedwhen the acid was applied in the form of the partial triethylammoniumsalt. It is evident from run 5 and from other experiments thatpolycarboxylic acids may be reacted with cellulose when the acids arecompletely neutralized with triethylamine. By virtue of this surprisingresult, it is possible to apply to cotton a variety of carboxylic acidswhich are insoluble in aqueous systems as the free acids or partialsodium salts (i.e., up to a 1 Na per ZCOOH), and which areinsufficiently reactive with cellulose when neutralized to higher levelswith sodium (i.e., even though solubilized at levels of Na above 1 perZCOOH, polycarboxylic acids show relatively poor reaction withcellulose). The acids illustrated in runs 4 and 5 are insoluble both asfree acids and as half sodium salts; although solubilized at higherlevels of neutralization with sodium, they are not reactive withcellulose in this form. The basis for the beneficial effects (i.e.,improved reaction) illustrated with the acids of runs 2. and 3 is lessapparent. In both cases a higher extent of reaction is obtained from theapplication of the amine salt than is realized with the correspondingsodium salt (or any level of sodium salt).

Very similar results were obtained when trimethylamine or ammonia wereemployed in place of triethylamine. The latter is particularlyattractive since it may be employed in almost any ratio with thecarboxylic acid and since am: monia is available at low cost.

In addition to generating a higher extent of reaction of polycarboxylicacid with cellulose, the ammonium or alkylammonium salt of the aciddevelops a higher degree of wet wrinkle recovery; e.g., forpropane-1,2,3-tricarboxylic acid, 244 vs. 217 applied from amine saltvs. sodium salt; and for butane-l,2,3,4-tetracarboxylic acid, 250" vs.204 applied from amine salt vs. sodium salt.

EXAMPLE 5 Samples of cellulose were dissolved in cuprammonium hydroxide,cupriethylenediamine hydroxide, and benzyltrimethylamrnonium hydroxideto produce solutions containing 1-5 of cellulose by weight. Melliticacid and cyclopentanetetracarboxylic acid were introduced to the extentof 8-11% of the Weight of cellulose and the cellulose was regeneratedfrom this solution by coagulation with 9% solution of sulfuric acidcontaining 0.5% of zinc sulfate. The fibrous regenerated cellulose wasdried at room temperature and was found to be completely soluble in theoriginal solvents; however, insolubility in these solvents was developedwhen the regenerated cel lulose was heated for a period of 1-0 minutesat 150 C.

EXAMPLE 6 Five percent of tetrasodium butane-1,2,3,4-tetracarboxylatewas introduced into a cellulose xanthate solution on the basis of thecellulose content of the solution. The cellulose was regenerated byextrusion into a dilute solution of sulfuric acid containing zincsulfate (see Example 5) and the fibers were washed thoroughly with waterand dried in air. The product was soluble in cupriethylenediaminehydroxide but following a 5-minute treatment at 170 C., the fibers werecompletely insoluble in this solvent.

EXAMPLE 7 Cellulose modified by polycarboxylic acids as illustrated inthe preceding examples is characterized by the unique ability to resistwrinkling, crumpling, and creasing under ordinary conditions to which afabric is subjected during wear; however, these modified celluloses areamenable to introduction of new creases or removal of old creases atelevated temperatures. The temperatures normally required for theintroduction or removal of a crease into this wrinkle resistantcellulose are in the range of -225 C. for periods ranging from hours atthe lower end of the range to several seconds at the upper end of therange. A sample of cotton print cloth was modified withcyclopentanetetracarboxylic acid by the process described in Example 3.The modified fabric containing 6.3% of the acid residue as measured byweight gain was rinsed in 1 N hydrochloric acid; one half of the samplewas rinsed with dilute sodium carbonate solution. Each half was rinsedwith distilled water. The acidrinsed sample, designated H+ form, hadcarboxyl groups in the free acid form, and the sodium carbonate-rinsedsample, designated Na+ form, had the unesterified carboxyl groups insodium salt form. The samples of fabric were subjected to creasingtests; the durabilities of the creases were tested by subjecting thecreased samples to 5 laundering cycles in an automatic washer withconventional detergent. The creases were rated by the visual AATCCmethod, which gives the best crease a rating of 5 and the absence of acrease a rating of 1. The results are dehyde, dimethylolethyleneurea,dimethyloldihydroxytabulated. ethyleneurea).

Monsanto wrinkle Rating ofcrease Rec. (W+F) durabihty Wash-wear Fabricsample Wet Dry rating Ironing #1 Ironing #2 11* form 226 272 4. 7 4. 74. 7 Na form l 195 248 4. 7 4. 7 4. 8 Dimethylolethylene urea- 5. 1.0 1. 0 Unmodified cotton 172 183 1. 0 3. 7 3.

at the linen setting; the operation was repeated for a second time.

It is apparent in the table above that the cotton fabric modified withcyclopentanetetracarboxylic acid exhibits enhanced wrinkle recoveryvalues in both wet and dry conditions, that the wash-wear rating is good(5 is maximum), and that the ironing operations introduce good creasesinto this sample of fabric. By comparison, unmodified cotton showspresence of a moderate crease and the cotton crosslinked with aconventional reagent (i.e., dimethylolethyleneurea) shows completeresistance to introduction of a crease.

By subjecting the creased portion of the cyclopentanetetracarboxylicacid-modified cottons to ironing as above in the fiat condition, it waspossible to remove the crease to essentially the same extent as forunmodified cotton.

EXAMPLE 8 Cotton print cloth modified with mellitic acid to the extentof 5.4% weight gain was rinsed with 1 N hydrochloric acid andsubsequently with distilled water. The samples of fabric were ironedunder the conditions defined in Example 7 and the creased swatches werelaundered to delineate durability of the creases. One portion of thecreased sample (prior to durability tests) was ironed flat and then putthrough the laundering cycles to measure the extent to which the creasecould be removed. The results are tabulated hereafter.

Measurements of crease durability on 2 Crease angles were measured by anadaptation of the Monsanto wrinkle recovery instrument. The smallerangles indicate the better crease. A sample of fabric which wascrosslinked with dimethylolethylurea in the creased state exhibited acrease with an angle of 75.

It is apparent from the data in the above table that the cotton modifiedwith mellitic acid is amenable to reversible creasing, that the creaseis substantially superior to that of unmodified cotton, and that thelatter difference becomes more pronounced as the test for durability ofthe ($63.56 becomes more strenuous.

EXAMPLE 9 A variety of wrinkle-resistant crosslinked cottons was testedfor amenability to introduction of a crease under the general conditionsdescribed in Example 7.

Cotton modified with polycarboxylic acids (e.g., those mentioned inpreceding examples and specifications) showed pronounced development ofdurable creases while cotton crosslinked with dibasic acids (i.e.,adipic acid) exhibited resistance to creasing as did also cottonscrosslinked with conventioned crosslinking agents (i.e., formal Weclaim:

1. A process for preparing a polycarboxylic acid-modified cellulose infibrous form comprising the following steps:

(a) impregnating fibrous cellulose with an aqueous solution of acarboxylic acid selected from the group consisting ofcyclopentanetetracarboxylic acid, nitrilotriacetic acid, mellitictrianhydride, pyromellitic acid, benzophenone-3,4,3,4'-tetracarboxylicacid, said aqueous solution having had substantially all carboxylic acidfunction neutralized with a strong base selected from the groupconsisting of ammonia, secondary amines, and tertiary amines, and

(b) heating the impregnated cellulose to produce the cellulose estersand to induce concurrent crosslinking of the cellulose.

2. The process of claim 1 wherein the polycarboxylic acid iscyclopentanetetracarboxylio acid.

3. The process of claim 1 wherein the polycarboxylic acid isnitrilotriacetic acid.

4. The process of claim 1 wherein the polycarboxylic acid is mellitictrianhydride.

5. The process of claim 1 wherein the polycarboxylic acid ispyromellitic acid.

6. The process of claim 1. wherein the polycarboxylic acid isbenzophenone-3,4,3,4'-tetracarboxylic acid.

7. A process comprising the following sequential steps:

(a) forming crosslinked cellulose esters of fibrous cellulose, whichcellulose is in the form of a textile fabric according to the process ofclaim 1,

(b) forming a textile article from the esterified and crosslinked fabricof step (a), and

(c) selectively installing or removing creases from the textile articleof step (b) via the simultaneous application of heat and pressure.

8. A process for preparing a polycarboxylic acid-modified cellulose infibrous form comprising the following steps:

(a) impregnating fibrous cellulose with an aqueous solution of acarboxylic acid selected from the group consisting ofcyclopentanetetracarboxylic acid, nitrilotriacetic acid, mellitictrianhydride, pyromellitic acid, benzophenone-3,4,3,4'-tetracarboxylicacid, said aqueous solution having had from approximately 0.01 to /2 ofall carboxylic acid function neutralized with a strong base selectedfrom the group consisting of alkali metal hydroxides, alkali metalcarbonates, alkali metal bicarbonates, alkali metal acetates, alkalimetal phosphates, and alkali metal borates, and

(b) heating the impregnated cellulose to produce the cellulose estersand to induce concurrent crosslinking of the cellulose.

9. The process of claim 8 wherein the polycarboxylic acid iscyclopentanetetracarboxylic acid.

10. The process of claim 8 wherein the polycarboxylic acid isnitrilotriacetic acid.

11. The process of claim 8 wherein acid is mellitic trianhydride.

12. The process of claim 8 wherein the polycarboxylic acid ispyromellitic acid.

the polycarboxylic acid is *benzophenone-3,4,3',4'-tetracarboxylic acid.

14. The ester of fibrous cellulose and a polycarboxylic acid selectedfrom the group consisting of cyclopentanetetracarboxylic acid,.nitrilotriacetic acid, mellitic trianhydride, pyromellitic acid,benzophenone-3,4,3',4'-tetracarboxylic acid, said esters beingcharacterized by a free car-boxylic content in the range of 25-80% ofthe total carboxyl groups in the initial polycarboxylic acid, and whichesters arevcharacterized by insolubility in water, aqueous. alkali, andorganic solvents. I. I Y

15. The fabric forrnof a fibrous cellulose acid polycarboxylate selectedfrom the group consisting of cellulose cyclopentanetetracarboxylate,cellulose nitrilotriacetate, cellulose mellitate, cellulosepyrornellitate and cellulose benzophenone 3,4,3,4-tetracarboxylate whichcellulose acid polycarboxylate is characterized by enhanced wrinkleresistance and the ability to develop or alternatively release creasesupon being brought into a new physical conformation at a temperaturewithin the range of about from 100 18. The fabric form of fibrouscellulose mellitate.

19. 'The fabric form of fibrous cellulose pyromellitate. 20.- The fabricform of fibrous cellulose benzophenone- 3,4,3',4'-tetracarboxylate. 1

References Cited UNITED STATES PATENTS 2,372,386 3/1945 Moncrief et a]812O X 2,759,787 8/1956 Touey et 211-. e 8l20 2,780,228 2/1957 Touey8l20 X 3,097,051 7/1963 Wade et al. I 8120 OTHER REFERENCES Gagliardi etal.: American Dyestu'fi Reported, pp. 74 79; Apr. 15, 1963. I 1

,Allen: Textile

